Abstract: BACKGROUND: Prostate cancer mortality is higher among black American men than among white American men. We investigated whether racial disparities in outcomes of clinically localized prostate cancer vary by treatment (surgery, radiation therapy, or nonaggressive treatment). METHODS: Merged Surveillance, Epidemiology, and End Results Program (SEER) and Medicare files provided data (on treatment modality, age, race, cancer stage, tumor grade, census tract socioeconomic status, and date of death) on 5747 black and 38 242 white patients diagnosed at age 65-84 years with clinically localized prostate cancer between 1986 and 1996 in five SEER sites. Patients were followed through 1998. Racial differences in survival outcomes were assessed using Kaplan-Meier survival curves and Cox regression models. RESULTS: The median survival time for black patients was 1.7 years (95% confidence interval [CI] = 1.6 to 1.9 years) less than that for white patients. Median survival in black patients relative to white patients was 1.8 years (95% CI = 1.5 to 2.0 years) less among those who had surgery, 0.7 years (95% CI = 0.5 to 1.0 years) less among those who had radiation therapy, and 1.0 years (95% CI = 0.7 to 1.1 years) less among those who had nonaggressive treatment. Racial disparities were evident both in overall survival and in prostate cancer-specific survival, before and after statistical adjustment for covariates. CONCLUSIONS: Black patients' poorer overall survival from localized prostate cancer varies by initial treatment, with the survival gap being largest among patients undergoing surgery. Investigating these treatment-specific differences may clarify the mechanisms underlying worse outcomes for black patients in the health care system.